Field of the Invention
The present invention relates to the field of biotechnology. More specifically, the invention relates to recombinant DNA molecules encoding enzymes that provide tolerance to herbicides that inhibit protoporphyrinogen oxidase.
Related Art
Agricultural crop production often utilizes transgenic traits created using the methods of biotechnology. A heterologous gene, also known as a transgene, can be introduced into a plant to produce a transgenic trait. Expression of the transgene in the plant confers a trait, such as herbicide tolerance, on the plant. Examples of transgenic herbicide tolerance traits include glyphosate tolerance, glufosinate tolerance, and dicamba tolerance. With the increase of weed species resistant to the commonly used herbicides, new herbicide tolerance traits are needed in the field. Herbicides of particular interest include herbicides that inhibit protoporphyrinogen oxidase (PPO), referred to as PPO herbicides. PPO herbicides provide control of a spectrum of herbicide-resistant weeds, thus making a trait conferring tolerance to these herbicides particularly useful in a cropping system combined with one or more other herbicide-tolerance trait(s).
Protoporphyrinogen oxidase functions in both chlorophyll and heme biosynthesis pathways where it converts protoporphyrinogen IX to protoporphyrin IX. Following production of protoporphyrin IX, the chlorophyll and heme biosynthetic pathways diverge with different metal ions being incorporated (iron for heme and magnesium for chlorophyll). Segments of this pathway are conserved across prokaryotes and eukaryotes, and many of the PPO enzymes found across prokaryotes and eukaryotes are relatively similar. Some prokaryotes (e.g., cyanobacteria) use this pathway for chlorophyll and heme production while other prokaryotes (e.g., Escherichia coli) use this pathway for heme production.
Herbicide-insensitive protoporphyrinogen oxidases (“iPPOs”) have been isolated from a number of prokaryotes and eukaryotes. On a structural basis, it is believed that there are at least three distinct subclasses of PPO enzymes: HemY (Hans son and Hederstedt, “Cloning and characterization of the Bacillus subtilis hemEHY gene cluster, which encodes protoheme IX biosynthetic enzymes” Journal of Bacteriology 174(24):8081-8093 (1992)), HemG (Sasarman, et al., “Mapping of a new hem gene in Escherichia coli K12” Microbiology 113:297-303 (1979)), and HemJ (Boynton, et al., “Discovery of a gene involved in a third bacterial protoporphyrinogen oxidase activity through comparative genomic analysis and functional complementation” Applied and Environmental Microbiology 77(14):4795-4801 (2011)). This invention provides novel recombinant iPPOs that are members of the HemG family. Despite twenty years of research and the number of iPPOs identified to date, a transgenic crop plant comprising a recombinant iPPO has yet to be commercialized. A strong weed control platform depends, in part, on continued development of herbicide tolerance trait packages. Identifying and utilizing iPPOs to create transgenic crop traits therefore represents an advance to agriculture.